The invention relates to mounting of an I/O bracket in a metal chassis of a computer system, and more specifically to a low EMI leakage solution to mounting an I/O bracket. Today's computer systems are required to connect to multiple peripheral devices such as external storage and network devices. Conductive pathways supported by input/output (I/O) panels in the computer chassis provide a means through which the input and output signals of the components in the chassis of the computer can communicate with peripheral devices external to the chassis.
Referring to FIGS. 1A and 1B show a partial view of a metal chassis 110 before insertion of an I/O panel 112 or I/O bracket 112 into the I/O frame 114 of the metal chassis 110. Typically for each I/O card, there is a corresponding opening in the rear of the metal chassis. It is well known that electronic components housed in the computer chassis are capable of emitting electromagnetic radiation and standards have been established for limiting such emissions. Openings in the metal chassis and leakage resulting from seams formed between two metal surfaces in the chassis can present particularly difficult problems with respect to such electromagnetic radiation.
Designs are typically made to minimize openings in the metal chassis and leakage due to seams. In the embodiment shown in FIG. 1A the openings 116 in the I/O frame are closed and the I/O panel 112 is secured to the I/O frame 114 by screwing the I/O panel 112 to the I/O frame 114. Although the implementation and assembly required by screwing the I/O panel to the I/O frame is simple, typically it does not provide a good EMI seal and the EMI rating of the closure required by FIG. 1A is not acceptable for all applications. The problem with the closure required by FIG. 1A, is that the differences in planarity between the metal I/O bracket retainer 118, the I/O frame 114 and the metal I/O panel 112 typically causes a seam to form along the edges of the I/O panel, resulting in EMI leakage. The solution of precisely machining the planarity of the parts so that no EMI leakage occurs is cost prohibitive. An alternative solution is to add a gasket between the metal I/O bracket retainer and the metal I/O panel.
In a second alternative embodiment, a gasketing layer 120 is positioned between the I/O bracket retainer 118 and the I/O panel of the metal chassis. FIG. 1B shows a partial view of a metal computer chassis before insertion of the gasketing layer 120 and I/O panel 112 into the I/O frame 114. Although the metal chassis 110 is typically comprised of sheet metal, typically the gasketing layer 120 shown in FIG. 1B is comprised of a stainless steel material. Conventionally the gasketing layer 120 is a thin layer of stainless steel, that typically has a thickness in the range of 0.15 to 0.3 mm. The gasketing layer 120 is typically dimpled so that it is nonplanar and conforms to the surfaces of the I/O bracket retainer 118 and the I/O panel 112. The gasketing layer 120 helps to eliminate any differences in planarity between the surface of the I/O bracket retainer 118 and I/O panel 112 by rubbing against the surfaces of the I/O bracket retainer and I/O panel sheet metal to ensure good contact is made, thus helping to eliminate any seams where EMI radiation leakage could occur.
Although the embodiment shown in FIG. 1B helps prevent EMI leakage, the configuration is more difficult to assemble than the embodiment shown in FIG. 1A. The gasket layering 120 must be carefully aligned so that the openings 116 of the I/O frame 114 coincide with the openings of the I/O panel and further that the screw hole for the gasketing layer are aligned to the corresponding screw holes of the I/O bracket and I/O frame. A further concern with related to the embodiment shown in FIG. 1B is design flexibility. Gasketing layers may need to be customized to fit a non-standard I/O opening potentially increasing computer system costs.
An I/O bracket retainer which is easy to assemble, takes minimal space and which provides design flexibility and excellent EMI shielding is needed.